Conventionally, in an AC electric motor, so-called current vector control has been performed in which current feedback control is performed on d and q axes. Patent Literature 1 discloses an example of a drive control device for an AC electric motor which performs such current vector control.
In the conventional drive control device for an AC electric motor disclosed in Patent Literature 1, different types of control are performed in a normal modulation region in which a pseudo sine wave voltage can be achieved by pulse width modulation and an over-modulation region in which a voltage is applied beyond the range of the normal modulation region. The control is performed to reduce a torque shock which occurs in the electric motor in transition from the normal modulation region to the over-modulation region. Current control is used in the normal modulation region while voltage control and square wave control are used in the over-modulation region to be changed according to the situation.